Zinc occurs commonly in nature as a sulfide intermixed with compounds of other metals. Various methods have been used in the past for obtaining zinc metals from such zinc ores. Zinc has been recovered by chlorination leaching of zinc containing ore by methods such as those taught in U.S. Pat. Nos. 1,736,659 and 1,838,857 to Mitchell, and 3,973,945 to Goens et al.
U.S. Pat. Nos. 1,736,659 and 1,838,857 of Mitchell disclose processes for the separation of metals from thin ores by chlorination leaching using CaCl.sub.2 and FeCl.sub.3 as the chlorinating agents with some chlorine being supplied by recycled chlorine. A problem presented in the processes of Mitchell is that the processes can start with iron sulfide present and when operated with iron chloride do not effectively remove the sulfur from the iron sulfide. The only method presented in the Mitchell processes for preventing further production of iron sulfide by the reaction of the free sulfur released from zinc is by maintaining strict control of the temperature at which the chlorination leaching is conducted.
U.S. Pat. No. 3,973,945 of Goens et al discloses a process for the removal of zinc from a zinc sulfide material using chlorination leaching in the presence of ferric ions. The process also discloses an iron cementation step for removing additional metal ions (other than zinc) present following chlorination and more importantly the conversion of the iron present in solution to the ferrous state. The iron must be in the ferrous state for the subsequent step of extracting the zinc from the solution. In the extraction step, the zinc chloride is extracted from the aqueous solution containing ferrous ions with an organic extractant such as a trialkylphosphate and tertiary amine. A problem with the process of Goens et al is that iron is necessarily added for the iron cementation step and a step must thereafter be added to the process for the removal of this iron to avoid contamination of the zinc product.